Regulation And Control Effects Of Water And Nitrogen Coupling On Photosynthetic Capacity Of Flue-cured Tobacco Seedlings At Transplanting Stage

During the production process of the northeast flue-cured tobacco, seedling survival rate when transplanted from greenhouse to field and cultivating seedling are the key factors to guarantee the production and quality of flue-cured tobacco. While water and nitrogen control in transplanting process are two important factors for flue-cured tobacco developing. Meanwhile, they are also key factors in the growth, yield and quality of flue-cured tobacco because they could influence soil nutrients condition and soil moisture condition. In our study, changes of photosynthetic gas exchange parameters, chlorophyll fluorescence parameters, antioxidant enzymes activities and osmotic adjustment substances were measured under different water and nitrogen coupling conditions. And the changes of photosynthetic characteristics of flue-cured tobacco seedlings were also studied in order to improve the quality of flue-cured tobacco seedling at transplanting stage. which could provide valuable data in cultivating seedling. The main results were as follows:1. Taking a flue-cured tobacco variety of Heilongjiang province "Longjiang911" as experimental material, the effects of different nitrogen fertilization rate on photosynthetic characteristics, chlorophyll fluorescence characteristics and antioxidant enzyme activity in seedlings were conducted to determine, when the flue-cured tobacco seedlings were grown in pots during the transplantation stage under drought stress. The results showed that the maximum photochemical efficiency (Fv/Fm), potential activities of PSⅡ (Fv/Fo) and the apparent electron transport rate (ETR) in leaves were decreased under drought stress, the proportion of energy which used for photochemical reaction were also reduced, and photoinhibition of photosynthesis occurred evidently under drought conditions, the photosystem Ⅱ (PSⅡ) reaction centre could be hurt. At the same time, the photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) in leaves of flue-curing tobacco were reduced, while intercellular CO2concentration (Ci) was first decreased and then increased under drought stress. Malondialdehyde (MDA), soluble sugar contents, SOD and POD activities were increased significantly under drought stress. A appropriate amount of nitrogen fertilizer application(0.36g·kg-2, pure nitrogen) could increase the opening degree in surplus activity center and maintain the stability of electron-transport chain. Pn, Gs,Tr, soluble sugar content, SOD, POD activities in seedlings of flue-curd tobacco treated by spraying0.36g·kg-1pure nitrogen fertilizer were all higher than CK under water stress, Ci and MDA were decreased. The appropriate amount of nitrogen fertilizer application also could improve the amount of light energy by capturing (φPo), the quantum yield for electron transport (φEo) and the electron transport efficiency of per reaction center(ETo/RC) in leaves of flue-cured tobacco seedlings. This indicated that the appropriate amount of nitrogen fertilizer application could protected the flue-cured tobacco photosynthetic apparatus from injury during drought, which could alleviate regulation of photosynthesis, maintaine cell membrane stability, increase osmolytes and antioxidant enzyme activity in seedlings of flue-cured tobacco. Meanwhile, appropriate amount of nitrogen fertilizer application could protected the flue-cured tobacco from injury during drought stress by increasing the heat dissipation, and observably improve the drought resistance of flue-cured tobacco seedlings. But over-fertilization of nitrogen (0.72g·kg-2, pure nitrogen) may cause reduction of the drought resistance of flue-cured tobacco seedlings.2. In flue-cured tobacco production process, water and nitrogen are two most important factors to limit the growth. The yield and quality of flue-cured tobacco couldnot be guaranteed without the combination these two factors. In order to explore the optimal water-nitrogen coupling model, the effects of water and nitrogen coupling on biomass, chlorophyll content, photosynthetic characteristics, chlorophyll fluorescence characteristics of flue-cured tobacco seedlings at transplanting stage were studied. The results found that the fresh and dry weights of leaf, and the fresh and dry weights of root were all showed a rising trend with the increase of soil moisture content. Chlorophyll content of flue-cured tobacco seedling in low water (W1) was lower than W2and W3. This proved that the synthesis of chlorophyll has close relationship with water content.In the three water content levels, Pn、Fv/Fm、Fv/Fo and ETR showed highest value under W2. This Result suggests that life condition of flue-cured tobacco is the most exuberant under intermediate moisture content water supply treatment.In different nitrogen levels, the indicators of flue-cured tobacco seedling processing were very different from each other. The fresh and dry weights of leaf, and the fresh and dry weights of root of flue-cured tobacco seedlings have reached the maximum values at middle nitrogen treatment (N1). At same time, the photosynthetic capacity, Fv/Fm、Fv/Fo and ETR of flue-cured tobacco seedlings were also the highest in nitrogen treatment(Nl). which indicated that proper amount of nitrogen has positive effects on tobacco growth, while excessive nitrogen fertilizer have no obvious effects, or even the opposite. In our study, N1W2(soil water content is55%±5%, pure nitrogen0.36g/kg,) was the optimal treatment, the yield and quality of flue-cured tobacco showed maximum improvements.